1. Field of the Invention
This invention relates generally to the device configuration and processes for manufacturing circuits on ceramic surface. More particularly, this invention relates to an improved configuration and process for manufacturing electronic circuits such as filters that includes inductor and capacitor formed on a spin-on-glass (SOG) coated ceramic substrate.
2. Description of the Prior Art
For those of ordinary skill in the art, the configurations and the process of forming circuits comprising metallic traces on a ceramic surface is still faced with the difficulties that the adhesion between the metal trace and the ceramic substrate surface is unreliable and the problem of peeling off becomes a quality issue and the circuits are not able to sustain long term reliable operations. These difficulties are specially pronounced in the processes of manufacturing the filters, e.g., band pass filter and low pass filters, where inductor and capacitor are formed on a ceramic substrate and the filters are designed to operate over many temperature cycles. The difficulties arise from the facts that the ceramic substrate has a very rough surface with uneven “peak and valley” surface profile. Metal traces, particularly metal traces of fine pitches with miniaturized dimensions when formed over these “peaks and valleys” tend not to have secure attachment to the surface. Poor adhesion of the circuit on the rough surface of the ceramic substrate becomes a major difficulty that prevent the implementation of a ceramic substrate to support electronic circuits such as filters that include capacitors and inductors where the precisely controllable capacitance cannot be produced due to the rough surface and poor adhesion difficulties.
Instead of ceramic substrate, convention technologies employ a specially glaze coated substrate where a glaze of a thickness of 50 μm. The glaze coated substrate has a smooth surface that can prevent metal traces from peeling off. However, the glaze-coated substrate is significantly more expensive than a bare ceramic substrate. Furthermore, the interface between a glaze-coated substrate and a ceramic carrier is hetero-junction. Due to the difference in thermal expansion coefficients, a temperature variation leads to bending of the substrate. For the purpose of employing processing steps with temperature cycles for manufacturing circuits such as a band pass filter (BFP), the problem of substrate deformations caused by differential temperature coefficients becomes a major disadvantage.
Therefore, a need still exists in the art of design and manufacture of electronic circuits such as inductors and capacitors (LC) for filters on ceramic substrate to provide a novel and improved device configuration and manufacture processes to resolve the difficulties. It is desirable that the improved configuration and manufacturing method can provide simplified processes to achieve lower production costs, high production yield while capable of providing electronic circuits that more compact with lower profile such that the circuits supported on a ceramic substrate can be conveniently integrated into miniaturized electronic devices. It is further desirable the new and improved circuits supported on new ceramic substrate and the manufacture method can improve the production yield with simplified configuration and manufacturing processes.